A refined methodology for stress inversions of earthquake focal mechanisms
A refined methodology for stress inversions of earthquake focal mechanisms
复制标题
地震震源机制应力反演的改进方法
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
M. Bohnhoff
中科院分区：
文献类型：
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作者：
P. Martínez‐Garzón;Y. Ben‐Zion;Niloufar Abolfathian;G. Kwiatek;M. Bohnhoff
我们开发了一种改进的方法，用于对二维或三维的背景应力场方向和应力比 R 进行震源机制的可靠高分辨率反演。地震目录被分簇，以消除可能受局部应力相互作用强烈影响的事件，而不是反映大尺度背景应力场。使用 k 均值算法将分簇数据离散化为包含最小数量 Nmin 和 2Nmin 之间的多个焦点机制的组。综合测试表明，当 R ≈ 0.5 时，Nmin 30 可在不同应力状态和噪声条件下提供稳定的反演结果，而当 R 接近 0 或 1 时，需要 Nmin 45。额外的综合测试比较了选择每个震源机制断层面的性能，使用（a）震源机构滑移矢量与应力张量剪切牵引之间失配角最小的平面和（b）不稳定程度最高的平面代表给定应力场和摩擦系数的最佳定向断层的接近度的系数。发现不稳定准则可以在所有测试的应力状态、应力比和噪声条件下提供更准确的反演结果。改进的反演方法将使用不稳定准则迭代选择断层面与不同震源机制组的阻尼同步反演相结合。表征阻尼反演期间合并的离散域邻域的结果提供了独立于离散化的高分辨率信息。该方法的某些方面通过南加州圣哈辛托断层带的震源机制数据进行了说明。
We develop an improved methodology for reliable high‐resolution inversions of focal mechanisms to background stress field orientation and stress ratio R in two or three dimensions. The earthquake catalog is declustered to remove events likely affected strongly by local stress interactions rather than reflecting the large‐scale background stress field. The declustered data are discretized with the k‐means algorithm into groups containing a number of focal mechanisms between a minimum number Nmin and 2Nmin. Synthetic tests indicate that Nmin ≈ 30 provides stable inversion results under different stress regimes and noise conditions when R ≈ 0.5, while Nmin ≈ 45 is needed for R near 0 or 1. Additional synthetic tests compare the performance of selecting the fault plane of each focal mechanism using (a) the plane with lowest misfit angle between the slip vector from the focal mechanism and shear traction from the stress tensor and (b) the plane with highest instability coefficient representing proximity to the optimally oriented fault for given stress field and friction coefficient. The instability criterion is found to provide more accurate inversion results under all tested stress regimes, stress ratios, and noise conditions. The refined inversion methodology combines selecting fault planes using the instability criterion iteratively with a damped simultaneous inversion of different focal mechanism groups. Results characterizing neighborhoods of discretized domains merged during the damped inversion provide high‐resolution information independent of the discretization. Some aspects of the methodology are illustrated with focal mechanism data from the San Jacinto Fault Zone in Southern California.